Phylum: Charophyta   Family: Closteriaceae

Closterium idiosporum  W. & G.S. West 1900

First described and illustrated by West & West (1900: 290, pl. 412: 6-7). There are two variety of Closterium idiosporum, this nominate variety and var. punctatum. They can only be reliably separated when found with the zygospores; rectangular in var. punctatum, elliptical in the nominate.
Cell dimensions: L: 17-248 µm; B: 4.8-7.7 µm; Ap: 1.5-2.4 µm; L/B: 28-34.
Zygospore dimensions: 44-48 x 22-24 µm.
Common in acidic moorland pools and loch-margins, also with Sphagnum.

References: 
Brook, A.J. & Williamson, D.B. (2010). A Monograph on some British Desmids.
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Van Westen, M. (2024). Sieralgen in Drenthe.
West, W. & West, G.S. (1900). Notes on freshwater algae. II.